t 105 ] 
fame quantity of motion j and therefore two heavy 
bodies in fuch cafes mull; always counterbalance each 
other. Now, this argument would be a juft one, if 
it could properly be faid, that the motion of the af- 
cending body was produced by that of the defending 
one ; but, fince the bodies are fo connected that one 
cannot poffibly begin to move before the other, I 
apprehend, that, if the bodies are fuppofed to move, it 
cannot be faid that the motion of one is produced by 
that of the other: fince whatever force is fuppofed to 
move one muft be the immediate caufe of motion in 
the other alfoj that is, both their motions muft be 
fimultaneous effects of the fame caufe, juft as if the two 
bodies were really but one. And therefore if I was 
to fuppofe, in this cafe, that the fuperior weight of 
the heavier body (which may be in itfelf much more 
than able to fuftain the lighter) fhould overcome the 
weight of the lighter and produce equal motions in 
both bodies ; I do not think that from thence I could 
be reduced to the abfurdity of fuppofing, that one 
body, by its motion, might produce in another, a mo- 
tion equal to its own, and yet not lofe its own at the 
fame time. But thofe who argue from the equality 
of motions on this occafion fay further, that, fince 
the two bodies muft have equal motions when they do 
move, they muft have equal endeavours to move even 
whilft they are at reft, and therefore thefe endeavours 
to move, being equal and contrary, muft deftroy each 
other, and the bodies muft continue at reft, and confe- 
quently ballance each other. In anfwer to this I muft 
obferve, that the abfolute force with which a heavy bo- 
dy endeavours to defcend from a ftate of reft can only 
be proportionable to its weight ; and therefore I think 
Vol. LIII, CL k 
